This product is a curved mirror (concave) with a base shape of a circle, offered by EKSMA Optics. The mirror has a diameter of 25.4 mm and a thickness edge of 6 mm. It is designed for use with a wavelength of 400 nm and features a protected silver coating on the front side, identified as "eks 0025protsil 4000". The mirror's geometry is spherical, with a radius of curvature (R1) of -800 mm, resulting in an effective focal length (EFL) of -400 mm. The material of the mirror is N-BK7 Schott, a popular choice for its excellent optical properties. According to the vendor's website, this item is currently in stock. For more detailed information, you can refer to the vendor's webpage provided in the item data.